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Blood

Blood is a fluid connective tissue becauseof the mesenchymal origin of its cells and

a low ratio of cells to liquid intercellular

substance, the blood plasma. In human

adults about 5 liter of blood contribute 7-8

% to the body weight of the individual.

Two Main Components: Plasma & Cells.

Blood Function to: Deliver Gases,

Nutrients, Hormones & Metabolic Wastes

to Different Sites.

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Blood

Plasma: Mainly Water (Exchange) &

Inorganic salts & Proteins. Proteins:Albumin, Globulin & Fibrinogen.

Albumin: Major protein, acts as Carrier.

Globulin:Act in formation of Antibodies. Fibrinogen: acts in formation of Fibrin or

Blood Clot during process of Blood

coagulation. The contribution of red blood cells

(erythrocytes) to the total volume of theblood (haematocrit) is about 43-45%.

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Methods of Study of Blood

Smear on Glass slide, Stained withRomanowsky Technique. Stains as Giemsa,Wright OR Leishman Method.

Features Obtained: Basophilia: Deep Blue: DNA,

Nuclei,Nucleolus,Ribosomes.

Azurophilia: Purple as Lysosomes of WBCs.

Eosinophilia: Eosin as in Hemoglobin of RBCs. Neutrophilia: No Stain as in Neutrophils.

Bone Marrow; Smear from Sternum, Stain

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Blood Formed Cells

Erythrocytes are the dominant (99%) butnot the only type of cells in the blood.

Leukocytes And, Blood Platelets.

Erythrocytes and blood platelets Perform

Their Functions Exclusively In The BloodStream.

In contrast, leukocytes reside only

temporarily in the blood. Leukocytes canleave the blood stream through the wallsof capillaries and venules and enter eitherconnective or lymphoid tissues.

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Reticulocytes

Fetal erythrocytes (up to the 4th Month Of

Gestation) are larger than "adult" erythrocytes,

and they are nucleated.

Then Nucleus extruded.

Reticulocytes Constitute up to 1% RBCs count.

Contain some Mitochondria & Ribosomes &

Golgi. Show Reticular precipitate R (Remnantof RNA)

Mature within 24 hrs of release into circulation.

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RBCs Functions

Erythrocytes function inthe transport of oxygen.

Haemoglobin, the oxygenbinding protein inerythrocytes, contributesabout 30% of the weightof an erythrocyte.

The lifespan of anerythrocyte in thebloodstream is 100-120

days.Spectrin is a structurapprotein that gives RBCtheir shape

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Leukocytes/WBCs

Leukocytes can be subdivided into:

Granular leukocytes, i.e. neutrophils, basophils and eosiniphils,and Non-granular leukocytes, i.e. monocytes and lymphocytes. A Differential Leukocyte Count: Count of different WBCs: ~ 60% Neutrophils (50% - 70%) ~ 3% Eosinophils (>0% - 5%)

~ 0.5% Basophils (>0% - 2%) ~ 5% Monocytes (1% - 9%) ~ 30% Lymphocytes (20% - 40%). Changes in their relative numbers indicate abnormality.

An increase number of neutrophils (neutrophilia) would indicatee.g. an acute or chronic infection. The number of basophils andeosinophils may increase (eosinophilia orbasophilia) as aconsequence of e.g. allergic disorders.

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Granular Leukocytes

Granular leukocytes are all approximately the

same size - about 12-15 m in diameter. Their nuclei form lobes, The number of nuclear

lobes varies according to cell type. All

Granulocytes Are Motile.

The term granulocytes refers to the presence of

granules in the cytoplasm of these cells. The

granules correspond to secretory vesicles and

lysosomes. Specific granules are the granuleswhich are only found in one particular type of

granulocyte.

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Neutrophils

Posses a very characteristic nucleus. It is divided into 3-5 lobes

which are connected by thin strands of chromatin. The number of lobes increases with cell age. Up to 7 lobes can

be found in very old neutrophils (hypersegmented cells). Neutrophils (like all other granulocytes, monocytes and lymphocytes)

contain all the organelles that make up a typical cell.

Also contain two types of granules. Primary Granules (Or A Granules) Contain Lysosomal Enzymes and

are likely to be primary lysosomes, although they are larger (0.4 m)than the "ordinary" primary lysosome.

Secondary Granules (Or B Granules), the specific granulesof the

neutrophils, contain enzymes with strongbactericidal actions. The specific granules of neutrophils stain only weakly if they are at all

visible - they are "neutral", hence the term neutrophil.

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Functions of Neutrophils

They are the First Wave Of Phagocytic Cells

invading sites of infection, and their

phagocytotic activity is stimulated if invading

microorganisms are "tagged" with antibodies

(opsonised). Neutrophils cannot replenish theirstore of granules. The cells die once their

supply of granules has been exhausted. Dead

neutrophils and tissue debris are the MajorComponents Of Pus. Their lifespan is only

About One Week.

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Eosinophil granulocytes

Nucleus usually has only Two Lobes.

Cytoplasm appears filled with the specific Red Colorgranules of The Eosinophils.

Contain usual organelles and some large rounded redColor granules (up to 1 m) in their cytoplasm.

The specific granules contain, in addition to enzymes thatotherwise are found in lysosomes,

Functions Their granules also contain the enzymes Histaminase And

Arylsufatase. These Enzymes Break Down Histamine And

Leukotrienes. The presence of antibody-antigen complexes stimulates the

immune system. Eosinophils phagocytose these complexes andthis may prevent the immune system from "overreacting".

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Basophil granulocytes (or basophils) Basophilic granulocytes have a 2 or 3 lobed nucleus.

The lobes are usually not as Well Defined Because Of

Abundant Granules. The specific granules of basophils are stained deeply

bluish or reddish-violet. The specific granules ofbasophils (about 0.5 m) appear quite dark in EMpictures. They contain heparin, histamine lysosomal

enzymes and leukotrienes (the later correspond to theslow-reacting substance of anaphylaxis or SRS-A).

Functions Heparin and histamine are Vasoactive Substances.

They dilate the blood vessels, make vessel walls more

permeable and prevent blood coagulation. As aconsequence, they facilitate the access of otherlymphocytes and of plasma-borne substances ofimportance for the immune response (e.g. antibodies)to e.g. a site of infection. The release of the contents of

the granules of basophils is receptor-mediated.

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Non-granular leukocytes

Monocytes

Nucleus Kidney Or Indented

Slightly larger than granulocytes (about 12-18 m in

diameter). Their cytoplasm stains usually sky clear blue

color. Functions

2ndLine Of Phagocytic Cells. Once monocytes enter the

connective tissue they differentiate into macrophages. At

sites of infection macrophages are the dominant cell type

after the death of the invading neutrophils. The

phagocytose microorganisms, tissue debris and the deadneutrophils. Monocytes also give rise to osteoclasts, which

are able to dissolve bone. They are of importance in bone

remodelling.

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Lymphocytes

These cells exit as Large or Small Lymphocytes. The smallestmay be smaller than erythrocytes (down to ~5 m in diameter)

while the largest may reach the size of large granulocytes (up to15 m in diameter). Small ones are the majority type in the blood, the nucleus may appear

to fill the entire cell. The typical lymphocyte only contains the usual complement ofcellular

organelles.). Functions

Most lymphocytes in the blood stream belong to either the group OfB-lymphocytes (~5%) Or The Group OfT-lymphocytes (~90%).

Upon exposure to antigens by antigen-presenting cells (e.g.macrophages) and T-helper cells (one special group of T-lymphocytes)

B-lymphocytes Differentiate Into Antibody ProducingPlasma Cells. Types: T-lymphocytes and B-lymphocytes form the major type oflymphocytes in the blood.

Natural killer (Nk-) cells which belong to the group of large type .Function to Attach Tumor Cells.

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Blood Platelets (or thrombocytes)

Smallest type of cells. Do not contain a nucleus.

Blood platelets are fragments of the cytoplasm of verylarge thrombocyte precursor cells, megakaryocytes.Like other cells involved in the formation in blood cells,megakaryocytes are found in the bone marrow.

Platelets are about 3 m long. Contain all types of Organellesdespite their small size. Contain, granules, mitochondria,ribosomes, lysosomes and a little ER.

Different types of vesicles contain eitherserotonin (electron-dense delta granules; few) or compounds important forBloodCoagulation(alpha granules - they also contain platelet-derived growth factor(PDGF) which may play a role in therepair of damaged tissue).

Contain also cytoskeletal fibres, which include actin and

myosin.

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F ti

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Functions Platelets Assist In The Arrest Of Bleeding. Serotonin is a potent vasoconstrictor. The release of serotonin

from thrombocytes, which adhere to the walls of a damagedvessels, is sufficient to close even small arteries.

Platelets, become "sticky" and activate other platelets to undergothe same transformation. This cascade of events results in theformation of a Platelet Plug(or platelet thrombus).

Finally, activating substances are released from the damagedvessel walls and from the platelets. These substances mediatethe conversion of the plasma proteinprothrombin intothrombin. Thrombin catalyzes the conversion offibrinogen intofibrin, which polymerizes into fibrils and forms a fibrous net in

the arising blood clot. Platelets function in Clot Retraction, which further assists inhaemostasis.

Decrease # Leads to impairment of haemostasis OR BleedingDisorders.